This invention relates to vapor phase equilibration and more particularly, to a novel crucible design for vapor phase equilibration between two solids.
In recent years, interest in forming active optical waveguiding structures has been stimulated by the need for optical modulators and deflectors, as well as for more efficient harmonic generators. To date, for device applications, experimental emphasis has been placed on those waveguides formed within, or on, single crystalline materials such as lithium niobates: J. M. Hammer and W. Phillips, Appl. Phys. Lett., 24, 545 (1974) I. P. Kaminow and J. R. Carruthers, Appl. Phys., Lett., 22,326 (1973); J. R. Carruthers, I. P. Kaminow and L. W. Stulz, Appl. Opt., 13, 2333 (1974); I. P. Kaminow, J. R. Carruthers, E. H. Turner, and L. W. Stultz, Appl. Phys. Lett., 22, 540 (1973); U.S. Pat. Nos. 3,837,827 and 3,911,176. Single crystalline materials such as the garnets have also been emphasized: P. K. Tien, R. J. Martin, S. L. Blank, S. H. Wemple, and L. J. Varnerin, Appl. Phys. Lett., 21, 207 (1972); P. K. Tien, R. J. Martin, R. Wolfe, R. C. LeCraw and S. L. Blank, Appl. Phys. Lett., 21, 397 (1972); and P. K. Tient and D. P. Schinke, J. Appl. Phys., 45, 2059 (1974).
Promising results have been obtained by forming a thin layer within a substrate such as, for example, by diffusion, ion exchange, or ion implantation. See, for example, the extensive reference list contained in P. K. Tien and A. A. Ballman, J. Vac. Technol., 12, 892 (1975). Vacuum out diffusion such as reported in the lithium niobate articles cited above produces a nonstoichiometric waveguide layer characterized by a large defect concentration of lattice vacancies and the formation of lithium deficient phases at, or near, the surface. Metal ion, in-diffused waveguides such as reported in the above cited articles on garnets and in R. V. Schmidt and I. P. Kaminow, Appl. Phys. Lett., 25, 458 (1974) and in J. Noda, T. Saku and N. Uchida, Appl. Phys. Lett., 25, 308 (1974) developed equivalent defect concentrations of lattice vacancies and usually leave a residual layer of nondiffused oxide on the surface.
Neither approach offers sufficient flexibility in adjusting either the magnitude of the refractive index change or the shape of the refractive index profile to provide reproducible results of the degree of stability required for stabilization and interchangeability of like components in fine tuned integrated optical circuitry.
The present invention is directed to the redesign of the constant activity multiple phase crucible developed by the inventor and reported in "Intrinsic and Extrinsic Nonstoichiometry in the Lead ZirconateTitanate System", Ph.D. Thesis, Univ. of Calif., Berkeley, 1972, (LBL880); "Intrinsic Nonstoichiometry in the Lead ZirconateLead Titanate System Determined by Knudsen Effusion", J. Appl. Phys., 44, 5227 (1973); and "Novel Uses of the ThermoMicrobalance in the Determination of Nonstoichiometry in Complex Oxide Systems", [J. Vac. Sci. Technol., 11, 434 (1974) to solve the reproducibility problem in optical waveguides and to control the magnitude and profile of the optical index of refraction therein; and, to achieve mass transport under vapor phase equilibrium conditions between solids having a common vapor phase whose vapor pressure is less than about 10.sup.-4 atm.